title: Impact of a routine two-dose varicella vaccination program on varicella epidemiology.
abstract: OBJECTIVE
  One-dose varicella vaccination for children was introduced in the United States in 1995. In 2006, a second dose was recommended to further decrease varicella disease and outbreaks. We describe the impact of the 2-dose vaccination program on varicella incidence, severity, and outbreaks in 2 varicella active surveillance areas.
  
  
  METHODS
  We examined varicella incidence rates and disease characteristics in Antelope Valley (AV), CA, and West Philadelphia, PA, and varicella outbreak characteristics in AV during 1995-2010.
  
  
  RESULTS
  In 2010, varicella incidence was 0.3 cases per 1000 population in AV and 0.1 cases per 1000 population in West Philadelphia: 76% and 67% declines, respectively, since 2006 and 98% declines in both sites since 1995; incidence declined in all age groups during 2006-2010. From 2006-2010, 61.7% of case patients in both surveillance areas had been vaccinated with 1 dose of varicella vaccine and 7.5% with 2 doses. Most vaccinated case patients had <50 lesions with no statistically significant differences among 1- and 2-dose cases (62.8% and 70.3%, respectively). Varicella-related hospitalizations during 2006-2010 declined >40% compared with 2002-2005 and >85% compared with 1995-1998. Twelve varicella outbreaks occurred in AV during 2007-2010, compared with 47 during 2003-2006 and 236 during 1995-1998 (P < .01).
  
  
  CONCLUSIONS
  Varicella incidence, hospitalizations, and outbreaks in 2 active surveillance areas declined substantially during the first 5 years of the 2-dose varicella vaccination program. Declines in incidence across all ages, including infants who are not eligible for varicella vaccination, and adults, in whom vaccination levels are low, provide evidence of the benefit of high levels of immunity in the population.
authors.affiliation: Centers for Disease Control and Prevention, 1600 Clifton Rd NE, MS A-34, Atlanta, GA 30333. sbialek@cdc.gov.
authors.forename: Stephanie R
authors.initials: SR
authors.lastname: Bialek
authors.forename: Dana
authors.initials: D
authors.lastname: Perella
authors.forename: John
authors.initials: J
authors.lastname: Zhang
authors.forename: Laurene
authors.initials: L
authors.lastname: Mascola
authors.forename: Kendra
authors.initials: K
authors.lastname: Viner
authors.forename: Christina
authors.initials: C
authors.lastname: Jackson
authors.forename: Adriana S
authors.initials: AS
authors.lastname: Lopez
authors.forename: Barbara
authors.initials: B
authors.lastname: Watson
authors.forename: Rachel
authors.initials: R
authors.lastname: Civen
mesh_terms: D000293:Adolescent; D000328:Adult; D002140:California / Q000453:epidemiology; D002644:Chickenpox / Q000175:diagnosis / Q000453:epidemiology* / Q000517:prevention & control*; D019433:Chickenpox Vaccine / Q000008:administration & dosage*; D002648:Child; D002675:Child, Preschool; D004196:Disease Outbreaks / Q000517:prevention & control*; D004334:Drug Administration Schedule; D005260:Female; D006801:Humans; D017589:Immunization Programs / Q000379:methods*; D007223:Infant; D008297:Male; D015143:Philadelphia / Q000453:epidemiology; D055815:Young Adult
chemical_list: D019433:Chickenpox Vaccine
keywords: United States/epidemiology; chickenpox vaccine; chickenpox/epidemiology; population surveillance; varicella vaccination; varicella/epidemiology